Innholdsfortegnelse for November/December 2017 i Australian Sky & Telescope

ROBERT MILLIKAN WAS a leading United States physicist of the early 20th century, who was awarded the Nobel Prize for Physics in 1923 for his famous ‘oil drop’ experiment by which he was able to measure the electric charge on a single electron. He had also done important work on the ‘photoelectric effect’, whereby electrons are released from a metal surface when light falls on it. Millikan’s interest in the effect had been sparked by the explanation put forward by Einstein (and for which he was awarded the Nobel Prize in 1921). Einstein had argued that a beam of light consists of tiny packets of energy called photons. Millikan was a conservative 19th-century type of physicist, and rejected such radical ‘quantum’ ideas. But after years of careful and laborious experiment…

ASTRONOMY 2018 YEARBOOK Wallace, Dawes & Northfield For more than a quarter of a century, the Astronomy yearbook series has been an essential companion for every self-respecting Australasian astronomer. Packed full of data, with extensive month-by-month detail of what’s visible in the night sky (planets, constellations, meteor showers, comets, minor planets and more), it will keep you going all year. Available now. $29.95 plus postage & handling 2018 AUSTRALASIAN SKY GUIDE Nick Lomb An ideal yearbook for beginners, the easy-to-read 2018 Australasian Sky Guide provides a month-by-month guide to what can be seen with the naked eye, along with lots of interesting facts and figures, detailed descriptions of special astronomical events, and planetary data. Available in November. Pre-order yours now! $16.95 plus postage & handling ASTRONOMY 2018 CALENDAR Featuring amazing…

» OUR SUN IS an average star about a third of the way through its lifetime. For most of a star’s existence, its colour and brightness depend almost entirely on how much hydrogen it was born with. Stars much more massive than our Sun are hot, bright and blue-tinted; stars less massive than ours are comparatively cooler, fainter and red-hued. The plot of colour (temperature) versus absolute brightness (luminosity) above, shows that most stars lie along a swath called the main sequence. (Our Sun is about midway along this arc.) Main-sequence stars are busy burning hydrogen in their cores. Red giants and supergiants, for their part, have stopped hydrogen core-burning. Instead, they host vast envelopes of gas that surround nuclear shell-burning layers around an inert, compact core. Plots like that…

I vividly remember the first time I saw NGC 253 , the Silver Coin Galaxy (also known as the Sculptor Galaxy). I was on a little weekend getaway with my family in the mountains, surrounded by trees, and not bad off in terms of light pollution. On the night in question, I was tired from an afternoon of swimming and hiking with my son, but still wanted to soak up a little starlight. So I grabbed my binos and popped into the lane behind the lodgings to see what was up. I was working on a list of deep sky binocular objects, and NGC 253 was one of my last remaining targets. My notes from that first observation hold up pretty well: “Outstanding, one of the best galaxies I’ve seen.…

Many of the brightest stars that make up the constellations are giants of one sort or another: blue Beta Centauri, yellow Canopus, orange Arcturus and red Gamma Crucis among them. But of the more-evolved pulsating red giants, only a few ever reach naked-eye brightness. Of these, the class prototype of the Mira variables, Mira itself, is the brightest. Mira was the first star to be identified (in the 1600s) as a periodic variable, yet despite centuries of observation it is still very much worth studying. Mira is a binary system about 300 light-years from Earth, with the companion (Mira B) being a white dwarf. Scientists have determined that Mira A has a hugely distended gas envelope 500 times the diameter of the Sun. The star ‘shakes’ as it pulsates, wobbling…

The fuming odd couple that is R Aquarii threw off a ring of hydrogen about 250 years ago. The ring shows hints of being the neck of a larger hourglass shape. Inside it, a pair of hot jets stab up and down from the goings-on at the centre. The frame above is about 4 arcminutes (0.9 light-year) wide. NATURE UNFOLDS IN UTTER tranquility, living out the endless trajectories of physics and all its derivative laws with minute precision — though with complete disregard for the feelings of little egos like us who find ourselves embedded within it. “Happiness is functioning the way a being is organised to function,” wrote Robert A. Heinlein, and the stars are serene in their courses. But it’s easy to imagine that some stars would be…

CANADA’S MALLINCAM, best known for producing sensitive analogue video-astronomy cameras, is now dipping a toe into the digital world. One of the company’s recent offerings, the SkyRaider DS2.3 Plus, is promoted as a versatile camera able to handle three types of astronomical imaging tasks: long-exposure deep sky, planetary, and video-assisted observing. That certainly piqued our interest. Could a single camera win the astrophotography trifecta? We contacted the company to borrow a unit and have a closer look. The SkyRaider is a cylindrical camera weighing 420 grams and is about as large as many of those 2-inch ultra-wide-field eyepieces coming out of Asia these days. It’s built around a Sony 2.35-megapixel IMX302 colour CMOS sensor with an array of 1,920-by-1,200 5.86-micron-square pixels. The camera employs a cooling fan to reduce thermal…

A TEAM OF AMATEUR OBSERVERS, some armed with just 75-mm telescopes, has found that the main-belt asteroid 113 Amalthea probably has a small companion. Paul Maley, a retired NASA staffer and a key member of the International Occultation Timing Association, enlisted amateur observers in Texas to observe the March 14 occultation of a 10th-magnitude star by the 13th-magnitude asteroid. A ‘fence’ of 10 observing sites spread across the occultation’s predicted path yielded seven positive occultations and three ‘misses’. One of those misses (red track in diagram), by Sam Insana in Gila Bend, Arizona, fell between five positive occultation tracks to his north and two to his south. The two southern ones, recorded by Dave Eisfeldt and Dick Campbell (both with the Central Texas Astronomical Society), appear to correspond to interruptions…

MORE THAN 100 SEARCHES for extraterrestrial intelligence have been carried out since 1960, when Frank Drake first pointed an 26-metre dish connected to a tabletop shortwave radio receiver at two nearby stars. Many of these SETI efforts viewed only a handful of stars for a few hours. A few ambitious surveys covered much of the sky, but they listened at each spot for only a few minutes. Some of the most famous SETI experiments have concentrated on a relatively few nearby stars — ‘few’ meaning in the thousands at most — scrutinising them intently one by one. This approach assumes that the Milky Way is buzzing with thousands or millions of radio-signaling civilisations, all of whose transmitters are relatively weak. But there’s every reason to think that an opposite assumption…

WHEN Late October 11pm Early November 10pm Late November 9pm These are daylight savings times. Subtract one hour if daylight savings is not applicable. HOW: Go outside within an hour or so of a time listed above. Hold the map above your head with the bottom of the page facing south. The chart now matches the stars in your sky, with the curved edge representing the horizon and the centre of the chart being the point directly over your head (known as the zenith). FOR EXAMPLE: Look at the chart, and you’ll see that the bright star Canopus in the constellation Carina is about a third of the way between the southeastern horizon and the middle of the chart. So if you look into the south-eastern sky, you’ll find Canopus…

Two of my favourite meteor showers return in November and December. The last perihelion passage of the Leonids’ parent comet, 55P/Tempel-Tuttle, in 1998 is almost two decades ago now. Our knowledge of the comet’s dust ejection and trail evolution has greatly improved since then, due mainly to the work of Mikhail Maslov. According to his calculations there is a chance for a rather narrow trail of meteoroids to be released from the parent comet, reaching Earth on November 16 at 17:07 universal time (UT), with a zenithal hourly rate (ZHR) of about 10 to 12, composed of brighter meteors. The traditional maximum should occur on November 17 near 16:30 UT, also with a ZHR of 10 to 12. For Australian observers the radiant will be best placed after 3:00am, low…

A BIOLOGIST ONCE SAID THAT God must have an inordinate fondness for beetles because he made so many of them. The Almighty must also have loved impact craters, for millions of them adorn our Moon, other moons, asteroids, solid planets, and probably the surfaces of rocky exoplanets. I like impact craters too, and the Moon’s eons-old landscape is my favourite venue for admiring their variations. Over the last 60 to 70 years, the basic facts of impact crater formation have become well established. On the Moon, crater diameters range from micron-size zap pits to 1,000-km-wide basins, and their morphologies (shapes and characteristics) systematically change as their sizes climb. Lunar craters smaller than about 15 km across — such as 13-km Chladni — are commonly flat-floored bowls with smooth walls, looking…

Traveling to observe with Jimi Lowrey makes for a long day. It starts with two flight segments over six hours, whereupon Steve Gottlieb and I then rent a car for the three-hour final drive, so by the time we arrive at Jimi’s place, we’re tired. But that exhaustion evaporates quickly in his observatory, with the sky darkening and his 1.2-metre (48-inch) telescope ready for action. The 1.2-m is an alt-az f/4 Newtonian reflector controlled with a laptop computer. With the scope angled nearly horizontally when the observatory roof is closed, its back end, which supports the exquisitely figured primary mirror, is almost taller than I am. Best of all, this impressively large and well-made telescope is optimised for visual observing. We need a 5-metre-tall orchard ladder to reach the eyepiece…

HOW TO SUBMIT YOUR IMAGES Images should be sent electronically and in high-resolution (up to 10MB per email) to contributions@skyandtelescope.com.au. Please provide full details for each image, eg. date and time taken; telescope and/or lens; mount; imaging equipment type and model; filter (if used); exposure or integration time; and any software processing employed. If your image is published in this Gallery, you'll receive a 3-issue digital subscription or renewal to the magazine.…

On human timescales, it’s easy to think of the Solar System as stable and unchanging. But over the next 6.5 billion years, as the Sun swells into a red giant and goes on to become a white dwarf, its family of planets will undergo radical alterations. Mercury will evaporate into the Sun, and Pluto will develop lakes on its surface. There’s a chance life could arise in liquid seas on distant moons, that two or more of the inner planets could collide, or that some planets could be flung right out of the Solar System. For Earth in particular, all hell will break loose, with our beloved planet becoming a cinder devoid of all life, and possibly destroyed altogether. Only time separates us from this destiny. Fortunately, there’s lots of…

Tracking variable stars requires meticulous observation habits, with careful attention paid to a single characteristic of a star — its brightness. Many amateur astronomers lean toward observing larger, richer, more detailed or more colourful deep sky objects, presuming that monitoring variable stars requires more work or more prolonged effort than they want to put out. So you may be surprised to learn that three of the greatest amateur astronomers of the 20th century, all widely famed for their interest in more visually rich classes of astronomical objects, all widely treasured for their skilled and beautiful astronomical writing, were devoted, masterful and passionate observers of variable stars. These three great amateur astronomers are, in chronological order: William Tyler Olcott, Leslie Peltier and Walter Scott Houston. It is interesting to ponder the…

Over the years, I’ve observed more than 60 doubles in Aries, half of them brighter than 10th magnitude and within reach of 20 cm telescopes. First up this month is, 1 Arietis , STF 174 , about 1.5 degrees northwest from Beta Ari (mag 2.6). The stars are slightly unequal in brightness, and with a 140-mm refractor were just separated at 114×. Hartung commented on the colour contrast, deep yellow and white. A genuine binary, STF 174 has shown very little change since the measure by F.G.W. Struve in 1830. Gamma Arietis is the 3rd-brightest in the line of naked-eye stars that mark Aries. A lovely object even with 80 mm, with 140 mm it showed as equal, pale yellow, bright stars, with 62× showing them neatly separated. It has…

A bright planet usually attracts attention in the late night long before it comes to opposition. But you have to be dedicated to net dim Uranus and Neptune before they become conveniently placed in the evening sky. Which, for the next decade or so, will mean spring and early summer. Neptune, magnitude 7.8 in Aquarius, was at opposition on September 5. Uranus, in Pisces, came to opposition on October 19. At magnitude 5.7, Uranus is detectable with the naked eye if you have a good dark sky. Both planets are in the ‘Great Water’ region, over which the Great Square of Pegasus reigns. The edge of the Great Square just made it into the top of our wide-field chart on the facing page, which shows stars to 7th magnitude. That’s…

Beneath Orion’s foot Eridanus begins His winding course, and reaches Cetus’ fins. — Aratus, Phaenomena, translated by John Lamb 1848 ACROSS THE AGES, the constellation Eridanus, the River, has been portrayed with surprising variety. Arguably, its most captivating depiction appears in the beautiful edition of Phaenomena published in 1600 by Hugo Grotius and called Syntagma Arateorum. Its illustrations were inspired by an illuminated manuscript Grotius possessed, and their superb execution was carried out by engraver Jacob de Gheyn. In turn, de Gheyn’s engraving style influenced Johann Bayer’s magnificent pictorial atlas, Uranometria. In Syntagma Arateorum, a starry river-god personifies Eridanus, his waters spilling from an urn and swirling around him. Although the river god himself is bedecked with stars, the further depths of this swath of sky abound with the celestial…

THE 2018 NATIONAL AUSTRALIAN Convention of Amateur Astronomers (NACAA) will be held in the Victorian regional city, Ballarat, over the Easter weekend, March 30–April 2. NACAA aims to bring together amateur (and not-so-amateur) astronomers from Australia, New Zealand and beyond to share in learning, disseminating and planning cutting-edge astronomical work in the region. As always, the event will span a full long weekend, Friday to Monday, encompassing various presentations, workshops, symposia and posters, covering a great width of astronomical work including observing, instrumentation, education, research, history and local activities. There is truly a vast amount of important astronomical activity undertaken by amateur astronomers in Australasia. NACAA is an opportunity for those amateurs to share their knowledge with the broader community. The standard of work is such that collaboration also occurs…

IT WAS BEING BILLED as the ‘eclipse of the century’. Not since 1979 had the Moon’s umbra passed across the width of the USA to bring totality to so many millions of people. A substantial partial eclipse would also be visible over the entire North American continent, Central America and the northern half of South America. As expected, the demand (and prices) for accommodation on, or near, the centreline was high. To avoid this, six members of the Astronomical Society of Victoria (ASV), myself included, opted to take a package of accommodation in Denver (well south of the track) and day trip north by coach to the centreline in Douglas, Wyoming, where totality would last 2 minutes and 29 seconds. We enjoyed quality accommodation in down-town Denver at a discounted…

 WHEN AMATEUR ASTRONOMERS daydream, we often think about our next purchase. But I’ll bet many also muse about a prize that can’t be bought. Typically it requires loads of time at the eyepiece — or at the computer examining digital files — and a whopping dose of luck. I’m referring to the discovery of a new comet, asteroid, supernova or nebula. Most of us will live out our astronomical lives without ever fulfilling such a fantasy. Find yourself an unnamed object and bestow a snappy moniker on it. But I’ve got an easier way, albeit less thrilling, to ensure one’s astronomical legacy — name an object! If a target visible through the average amateur eyepiece readily takes the shape of something or someone most people would recognise, it probably has…